Pressure-induced structural transitions and electronic topological transition of Cu2Se

We performed high-pressure in situ angle dispersive X-ray diffraction (ADXRD) experiments combined with CALYPSO methodology and band structure calculations on Cu2Se up to 42.1 GPa at room temperature, and four phases were identified. The initial low-pressure phase is assigned to the previously proposed monoclinic structure (space group C2/c). Phase II (space group C2/m) and phase III (space group C2/m) emerged at 3.3 GPa. Moreover, a bulk metallic phase IV (space group Pca2(1)) emerged at 7.4 GPa. We find that, unexpectedly, semimetallic phase III probably experiences a pressure-induced electronic topological transition (ETT) to another semimetallic state at about 20.0-25.0 GPa. Our results show that pressure plays a dramatic role in tuning Cu2Se's crystal structures and electronic states. (C) 2017 Elsevier B.V. All rights reserved.